The invention relates generally to power conversion systems, and more specifically to a power conversion system and method that may be adapted for use in connection with an electro-chemical process.
Electro-chemical processes include processes where metal is deposited on a substrate by passing a current through an electrolyte. A typical electro-chemical cell such as an electrolyzer may include an anode, which is the source of the material to be deposited. An electrolyte, which is a medium through which metal ions are exchanged, may also be included. An electrolyzer may further include a cathode, which may comprise the substrate to be coated. The anode may be connected to the positive terminal of a power supply and the cathode may be connected to the negative terminal of the power supply. When a voltage is applied between the anode and the cathode, positive metal ions from the electrolyte are attracted to the cathode and deposited thereon. As replenishment for these deposited ions, the metal from the anode is dissolved and transferred into the electrolyte to balance the ionic potential.
Electro-chemical process may be utilized for production of hydrogen. Water is charged with electric current during electrolysis, to split water into hydrogen and oxygen. The charge breaks a chemical bond between the hydrogen and oxygen, creating charged particles called ions. Hydrogen is collected at the cathode and oxygen is collected at the anode. A voltage required for performing electrolysis, increases or decreases depending on change in temperature and pressure.
Electro-chemical processes may be characterized by specific requirements regarding the controllability, magnitude and quality of the direct current. Relatively large electro-chemical processes may require direct current of a magnitude of many kilo-amperes with relatively small ripple content. Electro-chemical processes may also benefit from a galvanic isolation of the process from a power supply grid that provides power to the process to enable an independent electric safety concept for the electro-chemical process. Galvanic isolation may reduce the circulation of undesired currents through the plant equipment.
Conventional power conversion systems may comprise power converters with a grid isolation transformer and an active thyristor-based step-down rectifier provided between the power supply grid and the process side. However, conventional power conversion systems may suffer from poor power quality typically associated with the inability to adjust the input power factor and harmonic content of the input currents. In the conventional power conversion process, AC power at fundamental grid frequency is converted to low voltage DC power. Due to operation at the typically low grid frequencies, relatively heavy and bulky transformers may be needed. Conventional power systems are also characterized by the fact that the electro-chemical process is controlled by active power semiconductors placed in the process current path. Since the process current is typically very high this requires active devices with a very high current carrying capability and leads to high power conversion losses.
Accordingly, a technique is desirable that helps in the achievement of high power quality and power factor while avoiding active semiconductors in the high current path.